I. Field of the Disclosure
The disclosure relates generally to adjustable attenuators. More specifically, the disclosure relates to digital step attenuators.
II. Background
A communication system may include various types of attenuators to control the signal strength of a signal applied to a particular portion of the communications system. As an example, an attenuator may be used to reduce the power or amplitude of a signal applied to an input of test equipment, gain/attenuator controlling elements, and automatic leveling/power control subsystems. Attenuators may protect receiving devices and match impedances. For example, adjustable attenuators may be used to lower the amplitude of a signal to a known amount to enable measurements or protect a receiving device from damage. In some applications, an attenuator may be used to match impedances by lowering an apparent standing wave ratio (SWR).
In current designs, a number of binary weighted switchable attenuator stages are cascaded in series to create a digital step attenuator. Each binary weighted switchable attenuator stage has just two states. For example, a binary weighted switchable attenuator stage may switch between 0 dB and 1 dB or 0 dB and 2 dB or 0 dB and 4 dB. As a result, each bit of control may add to the insertion loss of the binary weighted switchable attenuator stage based digital step attenuator. Gain stage accuracy during transitions between control words may limit the attenuator step accuracy of the binary weighted switchable attenuator stage based digital step attenuator.
Accordingly, there is a need for an improved digital step attenuator architecture having reduced insertion loss and improved attenuator gain step accuracy.